Grass Valley Maestro Master Control Reference Manual v.2.4.0 - Manual (Page 175)

MAESTRO — Automation Interface Protocol Technical Reference Manual 175
Typical Pitfalls
Maestro: 04 (b) ACK
Automation: 09 (c) TEN
Maestro: 05 (d) NAK - problem begins here
Automation: 02 02 22 45 97 (e) Query TX_STAT
Maestro: 04 ACK
Automation: 09 TEN
Maestro: 02 03 23 45 03 92 (f) TX_STAT = quiescent
Automation: 04 ACK
Automation: 02 02 22 45 97 (g) Query TX_STAT
Maestro: 04 ACK
Automation: 09 TEN
Maestro: 02 03 23 45 03 92 (h) TX_STAT = quiescent
Automation: 04 ACK
Automation: 02 06 7F 02 01 01 00 00 77 (i) Set TAKE_XPT PST -> 01
Maestro: 04 ACK
Automation: 02 02 A1 04 59 Set LRS_PST -> Stereo
Maestro: 04 ACK
Automation: 02 02 4C 01 B1 Set VID_MODE -> Cut
Maestro: 04 ACK
Automation: 02 03 91 01 06 65 Set PROLL -> 1.6 seconds
Maestro: 04 ACK
Automation: 02 02 44 80 3A (j) TX_TRIG (with preroll)
Maestro: 04 ACK
Automation: 02 02 22 45 97 (k) Query TX_STAT
Maestro: 04 ACK
Automation: 09 TEN
Maestro: 02 03 23 45 02 93 (l) TX_STAT = quiescent
Automation: 04 (m) ACK
Automation: 02 06 7f 02 02 02 00 00 75 (n) Set TAKE_XPT PST -> 02
Maestro: 04 ACK
The result of the above example was that source 02 (n) was transitioned to air rather than the expected source 01 (i) for the
following reason: Automation queried Maestro for TX_STAT at (a) which Maestro ACKnowledged receiving the request
at (b). When automation sent TEN (c), Maestro responded with NAK (d) indicating it had nothing to send (YET!). Auto-
mation again queried Maestro for TX_STAT (e) which Maestro ACKnowledged. When automation sent TEN, Maestro
responded (f) with quiescent. However, Maestro's response (f) was the response to the query at (a), NOT the query at (e).
In this case, automation was incorrectly handling a NAK response to a TEN resulting in all subsequent responses to be out
of sync with the queries by 1 command. Therefore, when automation later queries Maestro for TX_STAT (k) after the
TX_TRIG (j), the TX_STAT response (l) is actually queued from, and associated with, the TX_STAT query (g). Automa-
tion then immediately (and incorrectly) acted upon the quiescent TX_STAT and proceeded to change the PST source (n)
before the transition was complete resulting in the wrong source 02 on air. It is important to keep in mind that if Maestro
acknowledges a query, a response will be queued and returned to the automation system. A NAK in response to a TEN
when there are pending requests does NOT mean “Nothing to send”, but rather “Nothing to send YET”. It is also impor-
tant to remember that any pending requests for transition status (TX_STAT) should be read from Maestro buffers prior to
issuing a TX_TRIG to prevent processing of pre-transition status post-trigger.